Battery

ABSTRACT

A battery includes an anode having an alkali metal as the active material, a cathode having, for example, iron disulfide as the active material, and an increased electrolyte volume.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 13/668,917, filed onNov. 5, 2012, which is a divisional application of and claims priorityto U.S. Ser. No. 12/244,123, filed on Oct. 2, 2008, both of which arehereby incorporated by reference.

TECHNICAL FIELD

The invention relates to batteries, as well as to related components andmethods.

BACKGROUND

Batteries or electrochemical cells are commonly used electrical energysources. A battery contains a negative electrode, typically called theanode, and a positive electrode, typically called the cathode. The anodecontains an active material that can be oxidized; the cathode containsor consumes an active material that can be reduced. The anode activematerial is capable of reducing the cathode active material.

When a battery is used as an electrical energy source in a device,electrical contact is made to the anode and the cathode, allowingelectrons to flow through the device and permitting the respectiveoxidation and reduction reactions to occur to provide electrical power.An electrolyte in contact with the anode and the cathode contains ionsthat flow through the separator between the electrodes to maintaincharge balance throughout the battery during discharge.

One type of battery includes an alkali metal as the anode activematerial and iron disulfide as the cathode active material. The batterycan be a primary battery. Primary batteries are meant to be discharged(e.g., to exhaustion) only once, and then discarded. In other words,primary batteries are not intended to be recharged. Primary batteriesare described, for example, in David Linden, Handbook of Batteries(McGraw-Hill, 2d ed. 1995). In contrast, secondary batteries can berecharged for many times (e.g., more than fifty times, more than ahundred times, or more). In some cases, secondary batteries can includerelatively robust separators, such as those having many layers and/orthat are relatively thick. Secondary batteries can also be designed toaccommodate for changes, such as swelling, that can occur in thebatteries. Secondary batteries are described, for example, in Falk &Salkind, “Alkaline Storage Batteries”, John Wiley & Sons, Inc. 1969, andDeVirloy et al., U.S. Pat. No. 345,124.

SUMMARY

The disclosures relates to batteries, as well as to related componentsand methods. Sometimes, as a primary lithium battery including, forexample, FeS₂ as the cathode active material, discharges, the resultingproducts of the battery can occupy less volume compared to the initialreagents, resulting in an increased void volume (e.g., increasedporosity). If the amount of electrolyte in the battery is not adjustedfor the additional void volume that is created over the course ofdischarge, the battery would perform at less than optimal levels becausethe amount of electrolyte in the battery would not be sufficient to fillthe cathode pores, wet all of the active cathode surface, and promotetransportation of Li ions in the cathode matrix. Thus, the batteryperformance may degrade.

The invention generally relates to the recognition that for primarylithium batteries, such as Li/FeS₂ cells, a volume of electrolytegreater than a theoretical calculated minimum required volume forfilling pores in a cathode and separator, can improve cell performance.The volume of electrolyte required to fill cathode and separator porescan compensate for the change in cathode volume resulting from celldischarge. The volume of electrolyte can allow for full contact betweenthe electrolyte and the active cathode surface, and can transport Liions in the cathode matrix throughout the discharge process.

The additional void volume formed during discharge of the battery can becalculated from the electrochemical reaction that occurs when thebattery operates. In turn, the increase in void volume can be used tocalculate the theoretical minimum electrolyte volume or a ratio of theelectrolyte volume (v) to cathode active material mass (m) for a givenelectrochemical cell. The theoretical minimum electrolyte volume and thev to m ratio will be discussed further in the detailed description.

In one aspect, the invention features a method of making a battery. Thebattery includes a housing including an anode including an alkali metal,a cathode including a transition metal polysulfide, and a volume (v) ofan electrolyte. The method includes determining a total pore volume inthe battery prior to discharge, a void volume that will be generatedwhen the battery is discharged to exhaustion once, and adjusting thevolume (v) of electrolyte to greater than a sum of the total pore volumeand the void volume.

In another aspect, the invention features a battery including a housing.Within the housing are: an anode including an alkali metal; a cathodeincluding a mass (m) of a cathode active material including one or moretransition metal polysulfides having the formula M1_(a)M2_(b)S_(n); anda volume (v) of an electrolyte. M1 and M2 are transition metals, a+b isat least 1, and n is at least 2(a+b). The battery includes a total porevolume prior to discharge, a void volume that will be generated when thebattery is discharged to exhaustion, and the volume (v) of theelectrolyte is greater than the sum of the total pore volume and thevoid volume. In some embodiments, the invention features a primarybattery, where using the battery includes discharging but not rechargingthe battery.

Embodiments can include one or more of the following features.

In some embodiments, the battery has an electrolyte volume (v) totransition metal polysulfide mass (m) ratio of at least 0.33 ml/g and/orat most 0.5 ml/g. The mass (m) can be at least four grams and/or at mostsix grams. For example, the mass (m) can be at least 4.5 grams (e.g., atleast 4.97 grams). The v/m ratio can maintain ion transport in abattery.

In some embodiments, the battery (e.g., a AA battery) has a volume ofelectrolyte of at least 0.4 ml (e.g., at least 0.5 ml, at least 0.6 ml,or at least 0.7 ml) greater than the sum of the total pore volume andthe void volume. In some embodiments, the volume of electrolyte is atleast 1.4 ml and/or at most 2.2 ml. The amount of electrolyte canmaintain ion transport in a battery. The electrolyte can include two ormore ethers, which can form at least 95 percent by volume (e.g., atleast 97 percent by volume, at least 99 percent by volume) of theelectrolyte.

In some embodiments, the housing further includes a separator, which canhave a thickness of between 12 microns and 25 microns, a porosity ofbetween 37% and 70%, an area specific resistance of as low as 1 Ohm*cm²,and/or a tortuosity of as low as 1.3. In some embodiments, the housingis placed under vacuum, and the volume of electrolyte is placed into thehousing when the housing is under vacuum. In some embodiments, when thehousing is placed under vacuum, a volume of gas is removed from thecontents of the housing (e.g., the pores of the electrodes and theseparator).

The cathode can have a porosity of at most 35% (e.g., at most 30%, or atmost 25%). The transition metal polysulfide can include one or morematerials such as FeS₂, CoS₂, NiS₂, MoS₂, Co₂S₉, Co₂S₇, Ni₂S₇, Fe₂S₇,Mo₂S₃, and/or NiCoS₇. In some embodiments, the cathode can furtherinclude a material such as CuS, Cu₂S, FeS, CuO, Bi₂O₃ and/or CF_(x).

In some embodiments, the alkali metal is lithium. The lithium can bealloyed with aluminum, other alkali or alkali earth metals, or notalloyed with another metal.

In some embodiment, the battery can have an increased void volume duringdischarge. The electrolyte can compensate for at least 50% (e.g., atleast 75%, at least 95%) of the total increase in void volume. In someembodiments, the electrolyte compensates for 100% of the total increasein void volume. In some embodiments, the electrolyte can include alithium salt.

In some embodiments, the battery is a AA battery. The battery can be aprimary battery.

Embodiments can include one or more of the following advantages.

In some embodiments, a battery having an electrolyte to cathode activematerial (v/m) ratio of at least 0.33 ml/g and/or at most 0.5 ml/g canhave a better performance than a battery having an electrolyte tocathode active material ratio of less than 0.33 ml/g. In someembodiments, a battery having an electrolyte volume that is greater thanthe sum of the total pore volume and the void volume can have a betterperformance than a battery having an electrolyte volume that is equal toor less than the sum of the total pore volume and the void volume.

Other features and advantages will be apparent from the detaileddescription, the drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of an embodiment of a non-aqueouselectrochemical cell.

FIG. 2 is a graph showing an electrochemical cell performance as afunction of electrolyte fill ratio of an embodiment of a non-aqueouselectrochemical cell.

DETAILED DESCRIPTION

Referring to FIG. 1, a primary electrochemical cell 10 includes an anode12 in electrical contact with a negative lead 14, a cathode 16 inelectrical contact with a positive lead 18, a separator 20, and anelectrolyte. Anode 12, cathode 16, separator 20, and the electrolyte arecontained within a case 22 (e.g., a housing). Electrochemical cell 10further includes a cap 24 and an annular insulating gasket 26, as wellas a safety valve 28.

Cathode 16 includes a cathode current collector and a cathode materialthat is coated on at least one side of the cathode current collector.The cathode material includes cathode active material(s) and can alsoinclude one or more conductive materials and/or one or more binders.

The cathode material includes, for example, at least about 85% by weightand/or up to about 95% by weight of cathode active material. The cathodeactive material can include one or more transition metal polysulfideshaving the formula M1_(a) M2_(b) S., wherein M1 and M2 are transitionmetals, a+b is at least 1, and n is at least 2(a+b). In someembodiments, n is 2. In some embodiments, M1 and M2 are the sametransition metal. In other embodiments, n is greater than 2.5 (e.g.,greater than 3.0). Examples of transition metals include cobalt, copper,nickel, and iron. Examples of transition metal polysulfides include FeS₂(e.g., Pyrox Red 325 powder from Chemetall GmbH, which can includeadditives to offset or retard any buildup in acidity of the powder, suchas up to 1.5% by weight of calcium in form of calcium carbonate), CoS₂,NiS₂, MoS₂, Co₂S₉, Co₂S₇, Ni₂S₇, Fe₂S₇, Mo₂S₃, and/or NiCoS₇. Transitionmetal polysulfides are described further, for example, in Bowden et al.,U.S. Pat. No. 4,481,267 and Bowden et al., U.S. Pat. No. 4,891,283. Insome embodiments, the cathode active material includes a mixture ofdifferent transition metal polysulfides. In some embodiments, thetransition metal polysulfides are mixed with other cathode activematerials such as CuS, Cu₂S, FeS, CuO, CF_(x), MnO₂, V₂O₅, MoO₃, TiS₂,NbSe₂, NbSe₃, and/or Bi₂O₃.

In some embodiments, when the transition metal polysulfide is FeS₂, theFeS₂ is a powder having a particle size sufficiently small that ofparticles will pass through a sieve of Tyler mesh size 325 (sieveopenings of 0.045 mm). (The residue amount of FeS₂ particles not passingthrough the 325 mesh sieve is 10% max.) The Pyrox Red 325 FeS₂ can havean average particle size of between about 20 and 26 microns and atypical BET surface area of about 1.1 m²/g and density of 4.7 gm/cm³.

In some embodiments, the cathode active material further includes smallamounts of impurities. For example, the cathode active material can haveabout zero weight percent (e.g., at least one weight percent, at leasttwo weight percent, or at least three weight percent) and/or at mostfour weight percent (e.g., at most three weight percent, at most twoweight percent, at most one weight percent) of impurities.

The cathode active material can have a mass (m) of at least four grams(g) (e.g., at least 4.5 grams, at least five grams, or at least 5.5grams) and/or at most six grams (e.g., at most 5.5 grams, at most fivegrams, or at most 4.5 grams) in an electrochemical cell.

The conductive materials can enhance the electronic conductivity ofcathode 16 within electrochemical cell 10. Examples of conductivematerials include carbon black, graphitized carbon black, acetyleneblack, and graphite. In some embodiments, when the conductive materialis graphite, the graphite can be available under the trade designationTIMREX KS6 graphite from Timcal America. TIMREX graphite is a relativelyhigh crystalline synthetic graphite, BET surface area 20 m²/g, density2.25 g/cm³. (Other graphites can be employed selected from natural,synthetic, or expanded graphite and mixtures thereof) The carbon blackcan be an acetylene black available under the trade designation Super Pconductive carbon black (BET surface area of 62 m²/g, bulk density inbag 0.160 g/cm³′) from Timcal Co. Super P acetylene black has a pH ofabout 10 as measured by ASTM D1512-95. The cathode material includes,for example, at least about 3% by weight and up to about 8% by weight ofone or more conductive materials.

The binders can help maintain homogeneity of the cathode material andcan enhance the stability of the cathode. In some embodiments, thebinders are film-formers, and can have good affinity and cohesiveproperties for the cathode active materials and conductive materials.The binders can be chemically stable when exposed to an electrolyte.Examples of binders include linear di- and tri-block copolymers.Additional examples of binders include linear tri-block polymerscross-linked with melamine resin; ethylene-propylene copolymers;ethylene-propylene-diene terpolymers; tri-block fluorinatedthermoplastics; fluorinated polymers; hydrogenated nitrile rubber;fluoro-ethylene-vinyl ether copolymers; thermoplastic polyurethanes;thermoplastic olefins; styrene-ethylene-butylene-styrene blockcopolymers (e.g., Kraton G1651 elastomer from Kraton Polymers, Houston,Tex.); and polyvinylidene fluoride based polymers (Kynars). The cathodematerial includes, for example, at least about 1% by weight and/or up toabout 6% by weight of one or more binders.

The cathode current collector can be formed, for example, of one or moremetals and/or metal alloys. Examples of metals include titanium, nickel,and aluminum. Examples of metal alloys include aluminum alloys (e.g.,1N30, 1230, 1145, 1235) and stainless steel. The current collectorgenerally can be in the form of a foil (for example, a continuous solidsheet without apertures) or a grid. The foil can have, for example, athickness of up to about 35 microns and/or at least about 10 microns.

While electrochemical cell 10 in FIG. 1 is a primary cell, in someembodiments a secondary cell can have a cathode that includes theabove-described cathode active material.

Cathode 16 can be formed by first combining one or more cathode activematerials, conductive materials, and binders with one or more solventsto form a slurry (e.g., by dispersing the cathode active materials,conductive materials, and/or binders in the solvents using a doubleplanetary mixer), and then coating the slurry onto the currentcollector, for example, by extension die coating or roll coating. Theslurry coating on the current collector can then be dried in aconventional convective air oven to evaporate the solvents. Then acoating of the wet slurry can optionally also be applied to the oppositeside of the current collector. In such case the wet coating on theopposite side of the current collector is similarly dried in aconvective air oven to evaporate solvents. The coated current collectorcan then be calendered resulting in a compacted smooth dry cathodecoating having a desired thickness and porosity on a current collector.

In some embodiments, to form the slurry, solvents are first mixed withbinder to form a binder/solvent mixture. Cathode active materials andcarbon particles can be separately premixed and then added to thebinder/solvent mixture. The solvents can include a mixture of C₉-C₁₁(predominately C₉) aromatic hydrocarbons available as ShellSol A100hydrocarbon solvent (Shell Chemical Co.) and a mixture of primarilyisoparaffins (average M.W. 166, aromatic content less than 0.25 wt. %)available as Shell Sol OMS hydrocarbon solvent (Shell Chemical Co.). Theweight ratio of ShellSol A100 to ShellSol OMS solvent is desirably at a4:6 weight ratio. The ShellSol A100 solvent is a hydrocarbon mixturecontaining mostly aromatic hydrocarbons (over 90 wt % aromatichydrocarbon), primarily C₉ to C₁₁ aromatic hydrocarbons. The ShellSolOMS solvent is a mixture of isoparaffin hydrocarbons (98 wt. %isoparaffins, M.W. about 166) with less than 0.25 wt % aromatichydrocarbon content. The slurry formulation can be dispersed using adouble planetary mixer. Dry powders (e.g., FeS₂ powder and carbonparticles) are first blended to ensure uniformity before being added tothe Kraton G1651 binder solution in the mixing bowl. The solvents arethen added and the components blended in the mixer and until ahomogeneous slurry mixture is obtained.

In some embodiments, the cathode slurry includes 2 to 4 wt % of binder(Kraton G1651 elastomeric binder from Kraton Polymers, Houston Tex.); 50to 70 wt % of active FeS₂ powder; 4 to 7 wt % of conductive carbon(acetylene carbon black and/or graphite); and 25 to 40 wt % ofsolvent(s).

In certain embodiments, calendering can result in the reduction of poresin the cathode material of a cathode. These pores can, for example,permit an electrolyte to diffuse within a battery including the cathode.The diffusion of the electrolyte can, in turn, result in enhancedelectrochemical performance of the battery. In some embodiments, thecathode material of a cathode can have a porosity of at least about 18percent (e.g., at least about 20 percent, at least about 25 percent, orat least about 30 percent) and/or at most about 35 percent (e.g., atmost about 30 percent, at most about 25 percent, or at most about 20percent). In certain embodiments, the cathode material of a cathode canhave a porosity of from about 20 percent to about 30 percent. As usedherein, the porosity of the cathode material of a cathode is equal tothe percent by volume of the cathode material that is occupied by pores.The porosity of the cathode material is calculated according to equation(2) below, in which V_(final)=volume of the final cathode, andV_(theo)=theoretical volume of the cathode material in the final cathodeminus the volume of the current collector:

$\begin{matrix}{{\%\mspace{14mu}{Porosity}} = {\frac{V_{final} - V_{theo}}{V_{final}}*100}} & (2)\end{matrix}$

Anode 12 includes one or more alkali metals (e.g., lithium, sodium,potassium) as the anode active material. The alkali metal may be thepure metal or an alloy of the metal. Lithium is the preferred metal;lithium can be alloyed, for example, with other alkali metals, analkaline earth metal, or aluminum. The lithium alloy may contain, forexample, at least about 50 ppm and up to about 5000 ppm (e.g., at leastabout 500 ppm and up to about 2000 ppm) of aluminum or other alloyedmetal. The lithium or lithium alloy can be incorporated into the batteryin the form of a foil. In some embodiments, the anode foil can have athickness of about 0.15 mm.

Alternatively, anode 12 can include a particulate material such aslithium-insertion compounds, for example, LiC₆, Li₄Ti₅O₁₂, LiTiS₂ as theanode active material. In these embodiments, anode 12 can include one ormore binders. Examples of binders include polyethylene, polypropylene,styrene-butadiene rubbers, and polyvinylidene fluoride (PVDF). The anodecomposition includes, for example, at least about 2% by weight and up toabout 6% by weight of binder. To form the anode, the anode activematerial and one or more binders can be mixed to form a paste which canbe applied to a substrate. After drying, the substrate optionally can beremoved before the anode is incorporated into the housing.

The anode includes, for example, at least about 90% by weight and up toabout 100% by weight of anode active material.

The electrolyte preferably is in liquid form, and can be placed into abattery housing including the cathode, the anode, and the separatorwhile the housing is under vacuum. The electrolyte has a viscosity, forexample, of at least about 0.2 cps (e.g., at least about 0.5 cps) and upto about 2.5 cps (e.g., up to about 2 cps or up to about 1.5 cps). Asused herein, viscosity is measured as kinematic viscosity with aUbbelohde calibrated viscometer tube (Cannon Instrument Company; ModelC558) at 22° C.

The electrolyte can include a variety of solvents. In some embodiments,the electrolytic solution or electrolyte can be in liquid, solid or gel(polymer) form. In some embodiments, the electrolyte can include anorganic solvent such as propylene carbonate (PC), ethylene carbonate(EC), dimethoxyethane (DME) (e.g., 1,2-dimethoxyethane), butylenecarbonate (BC), dioxolane (DX), tetrahydrofuran (THF),gamma-butyrolactone, diethyl carbonate (DEC), dimethyl carbonate (DMC),ethyl methyl carbonate (EMC), dimethylsulfoxide (DMSO), methyl formate(MF), sulfolane, or a combination (e.g., a mixture) thereof. In certainembodiments, the electrolyte can include an inorganic solvent, such asSO₂ or SOCl₂. In some embodiments, the electrolyte can include acombination of two or more ethers. The ether content can be at least 95vol % (e.g., at least 96 vol %, at least 97 vol %, at least 98%, or atleast 99 vol %) of a total volume of solvents used for electrolyteformulation.

In some embodiments, the electrolyte includes one or more salts (e.g.,two salts, three salts, four salts). Examples of salts include lithiumsalts, such as lithium trifluoromethanesulfonate (LiTFS), lithiumtrifluoromethane-sulfonimide (LiTFSI), lithium iodide (LiI), lithiumbromide (LiBr), lithium tetrafluoroborate (LiBF₄), lithium perchlorate(LiClO₄), and lithium hexafluorophosphate (LiPF₆). Additional lithiumsalts that can be included are described, for example, in Suzuki, U.S.Pat. No. 5,595,841. Other salts that can be included in the electrolyteare bis(oxalato)borate salts (e.g., (LiB(C₂O₄)₂)) and lithiumbis(perfluoroethyl)sulfonimide (LiN(SO₂C₂F₅)₂). Bis(oxalato)borate saltsare described, for example, in Totir et al., U.S. Patent ApplicationPublication No. US 2005/0202320 A1, published on Sep. 15, 2005, andentitled “Non-Aqueous Electrochemical Cells”. The electrolyte includes,for example, at least about 0.1 M (e.g., at least about 0.5 M or atleast about 0.7 M) and/or up to about 2 M (e.g., up to about 1.5 M or upto about 1.0 M) of the lithium salts.

In some embodiments, an electrolyte solution includes a mixture ofLi(CF₃SO₂)₂N (LiTFSI) salt dissolved in a solvent mixture of 1,3dioxolane (70-80 vol %) and sulfolane (20-30 vol %), as in commonlyassigned U.S. patent application Ser. No. 11/494,244. Pyridine in amountbetween about 0.05 and 1.0 wt. %, for example about 0.1 wt. %, is addedto the electrolyte to reduce the chance of minor amounts ofpolymerization of 1,3-dioxolane.

In some embodiments, the battery active materials have a volume that canincrease, decrease, or remain the same during battery discharge. Ageneral formula for calculating the change in active material volumeduring battery discharge can be as follows:wA+xB=yC+zDwhere A, B are reactants (e.g., battery active materials); C, D areproducts; and w, x, y, and z are stoichiometric coefficients. Theabsolute volume change (ΔV) of this reaction, which can be positive ornegative, can be expressed as:ΔV={y*MW_(C)/ρ_(C) +z*MW_(D)/ρ_(D) }−{w*MW_(A)/ρ_(A) +x*MW_(B)/ρ_(B)}where MW_(i) is a molecular weight of reactant or product “i” and ρ_(i)is a density of reactant or product “i”.

In some embodiments, a theoretical minimum electrolyte volume needed toobtain a satisfactory performance from battery discharge can becalculated. For example, the theoretical minimum electrolyte volume canbe obtained by adding the total pore volume in the electrochemical cell(defined as the sum of the volume of the pores in a separator and thevolume of the pores in the cathode) and the void volume created as thecell discharges. As discussed above, the void volume that is createdduring discharge is due to the difference in density between theproducts of the discharge reaction and the initial reagents.

As shown in Table 1, in a lithium-iron disulfide electrochemical cellhaving an overall reaction FeS₂+4 Li⁺→Fe+2 Li₂S, the volumes of thestarting materials and the products can be obtained from the molecularweights and densities of the starting materials and the final products.The percentage of change in volume for the reaction can then bedetermined. For the reaction above, the percent change in volume betweenthe starting materials and the products is −18.54%.

The absolute volume decrease for a battery having a FeS₂ loading of 4.97grams at 1.05V cutoff (or 0.9 V cutoff) can be determined from theampere-hour (Ah) for 1 Mol of reacted FeS₂, the absolute ΔV/Ah, and theAh for 1.05 V cut-off (or 0.9 V cut-off), according to Table 1 and theequations therein. Thus, for a battery having a 4.97 gram loading ofFeS₂, the ΔV for 1.05 V cut-off is −0.38 cubic centimeters (cc, ormilliliters (ml)) upon battery discharge, and the ΔV for 0.9 V cut-offis −0.43 cc upon battery discharge.

TABLE 1 Calculations for ΔV. Starting materials Products FeS₂ 4 Li⁺ Fe 2Li₂S Molecular weight (g) 119.975 27.756 55.847 91.884 Density (g/cc)4.7 0.534 7.86 1.64 Volume (cc) 25.53 51.98 7.11 56.03 Absolute ΔV (cc)= (V_(products) − V_(starting)_materials) −14.372${\Delta\; V\mspace{11mu}\left( {{relative}\mspace{14mu}{to}\mspace{14mu}{starting}\mspace{14mu}{materials}} \right)} = \frac{V_{products} - V_{{starting}\_{materials}}}{V_{{starting}\_{materials}}}$−0.1854 (or −18.54%) Ah for 1 Mol of reacted FeS₂ (Ah) 107.08 AbsoluteΔV/Ah (cc/Ah) = −0.1342 Absolute ΔV/Ah for 1 Mol of reacted FeS₂ Ah for1.05 V cut-off for a battery having a 4.97 gram 2.8 loading of FeS₂ (Ah)Ah for 0.9 V cut-off for a battery having a 4.97 gram loading of 3.2FeS₂ (Ah) ΔV for 1.05 V cut-off (cc) = (Absolute ΔV/Ah) × −0.38 (Ah for1.05 V cut-off) ΔV for 0.9 V cut-off (cc) = (Absolute ΔV/Ah) × −0.43 (Ahfor 0.9V cut-off)

To compensate for the decrease in volume in the cathode active material(i.e., the increased void volume), the amount of electrolyte can beincreased by at least the same volume as the increase in void volume. Asan example, for a battery having a 4.97 g loading of FeS₂ and adischarge cut-off of 1.05V where the void volume increase is 0.38 ml,the electrolyte fill volume should be increased by 0.38 ml.

Thus, in the above lithium-iron disulfide electrochemical cell, if thevolume of the pores in both separators is 0.3242 ml, the volume of poresin the cathode at 0% depth of discharge is 0.4107 ml, and the voidvolume created during discharge is 0.38 ml as calculated above, thetheoretical minimum volume required to obtain satisfactory performancewould be 1.11 ml. Surprisingly, it was observed that the actual minimumelectrolyte volume required to obtain satisfactory performance in thecell is much greater than the theoretical minimum volume. For example,the actual minimum electrolyte volume can be about 1.63 ml or greater toobtain satisfactory performance.

In some embodiments, the amount of electrolyte can be expressed by theratio of electrolyte volume (v) in the cell to cathode active material(e.g., FeS₂) mass (m). For example, in the above lithium-iron disulfideelectrochemical cell, the actual minimum v/m ratio is calculated as 1.63ml/4.97 g FeS₂=0.33 ml/g. In some embodiments, v/m ratios of greaterthan 0.33 ml/g can further improve electrochemical cell performance. Forexample, the electrolyte to cathode active material loading ratio can beat least 0.33 ml/g (e.g., at least 0.35 ml/g, at least 0.4 ml/g, atleast 0.45 ml/g) and/or at most 0.5 ml/g (e.g., at most 0.45 ml/g, atmost 0.4 ml/g, at most 0.35 ml/g).

The actual volume (v) of the electrolyte can be at most 2.2 ml (e.g., atmost two ml, at most 1.9 ml, at most 1.8 ml, at most 1.7 ml, at most 1.6ml, or at most 1.5 ml) and/or at least 1.4 ml (e.g., at least 1.5 ml, atleast 1.6 ml, at least 1.7 ml, at least 1.8 ml, at least 1.9, or at mosttwo ml). In some embodiments, the actual volume of the electrolyte in anelectrochemical cell is greater than the theoretical minimum electrolytevolume. For example, the actual electrolyte volume can be at least 0.2ml (e.g., at least 0.3 ml, at least 0.5 ml, at least 0.7 ml, at leastone ml) and/or at most 1.5 ml (e.g., at most one ml, at most 0.7 ml, atmost 0.5 ml, at most 0.3 ml) greater than the theoretical minimumelectrolyte volume.

Positive lead 18 can include stainless steel, aluminum, an aluminumalloy, nickel, titanium, or steel. Positive lead 18 can be annular inshape, and can be arranged coaxially with the cylinder of a cylindricalcell. Positive lead 18 can also include radial extensions in thedirection of cathode 16 that can engage the current collector. Anextension can be round (e.g., circular or oval), rectangular, triangularor another shape. Positive lead 18 can include extensions havingdifferent shapes. Positive lead 18 and the current collector are inelectrical contact. Electrical contact between positive lead 18 and thecurrent collector can be achieved by mechanical contact. In someembodiments, positive lead 18 and the current collector can be weldedtogether.

Separator 20 can be formed of any of the standard separator materialsused in electrochemical cells. For example, separator 20 can be formedof polypropylene (e.g., nonwoven polypropylene, microporouspolypropylene), polyethylene, a polysulfone, or combinations of theabove materials. The separator can have a thickness of between 12microns and 25 microns (e.g., between 15 and 23 microns, or between 15and 20 microns) and/or a porosity of between 37 and 70 percent (e.g.,between 40 and 70 percent, between 40 and 60 percent, between 50 and 70percent). The separator can have an area specific resistance of as lowas one Ohm*cm² (e.g., as low as two Ohm*cm², as low as three Ohm*cm², orabout 1.3 Ohm*cm²), and separator can have a tortuosity of as low as 1.3(e.g., as low as 1.5, as low as 1.7, or as low as 1.9). Separators aredescribed, for example, in Blasi et al., U.S. Pat. No. 5,176,968. Theseparator may also be, for example, a porous insulating polymercomposite layer (e.g., polystyrene rubber and finely divided silica).

Case 22 can be made of, for example, one or more metals (e.g., aluminum,aluminum alloys, nickel, nickel plated steel, stainless steel) and/orplastics (e.g., polyvinyl chloride, polypropylene, polysulfone, ABS,polyamide).

Cap 24 can be made of, for example, aluminum, nickel, titanium, orsteel, and can include one or more vents. The vents can be made ofaluminum or aluminum alloys, such as A15052.

To assemble the cell, separator 20 can be cut into pieces of a similarsize as anode 12 and cathode 16 and placed therebetween. In someembodiments, the anode, cathode, and separator are spirally wound. Anode12, cathode 16, and separator 20 are placed within case 22, and one endof case 22 is closed with cap 24 having one or more vents and annularinsulating gasket 26, which can provide a gas-tight and fluid-tightseal. Positive lead 18 connects cathode 16 to cap 24. Safety valve 28 isdisposed in the inner side of cap 24 and is configured to decrease thepressure within electrochemical cell 10 when the pressure exceeds somepredetermined value. The case can first be placed under vacuum (e.g., to10 mm Hg, 15 mm Hg, 27 mm Hg, or greater), and the electrolyte can thenbe added into the case while the case is under vacuum. An electrolytefilling station (available from HIBAR Systems Limited) can be used tofill cells with electrolyte while the cell is under vacuum. Methods forassembling an electrochemical cell are described, for example, in Moses,U.S. Pat. No. 4,279,972, Moses et al., U.S. Pat. No. 4,401,735, andKearney et al., U.S. Pat. No. 4,526,846.

Without wishing to be bound by theory, it is believed that greatervacuum within the housing is correlated with the amount of electrolytethat can be added into the housing, as a greater vacuum can remove moreair or other gas from any pores within the electrodes and separator inthe housing. For example, a housing under greater vacuum can includemore electrolyte, since a greater amount of air or other gas is removedfrom the housing and its contents (e.g., the pores within the cathodeand/or the separator). Greater vacuum within the housing can decreasethe amount of time necessary for electrolyte addition.

Other configurations of an electrochemical cell can also be used,including, for example, the button or coin cell configuration, theprismatic cell configuration, the rigid laminar cell configuration, andthe flexible pouch, envelope or bag cell configuration. Furthermore, anelectrochemical cell can have any of a number of different voltages(e.g., 1.5 V, 3.0 V, 4.0 V). Electrochemical cells having otherconfigurations are described, for example, in Berkowitz et al., U.S.Ser. No. 10/675,512, U.S. Pat. App. Pub. 2005/0112467 A1, and Totir etal., U.S. Pat. App. Pub. 2005/0202320 A1.

The following examples are meant to be illustrative and not to belimiting.

Example 1

AA size Li/FeS₂ test cells (49×12 mm) were produced. The cathode coatinghad a slurry composition as shown in Table 1. The slurry was coated viaroll coating technique on both sides of a sheet of aluminum foilsubstrate of thickness 1 mil (0.025 mm) without any openingtherethrough. The coated aluminum foil was dried by gradually adjustingor ramping up an oven temperature (to avoid cracking the coating) froman initial temperature of 40° C. to a final temperature not to exceed130° C. for about 7-8 minutes or until the solvent has substantially allevaporated (At least about 95 percent by weight of the solvents areevaporated or at least about 99.9 percent by weight of the solvents areevaporated). The dried coated aluminum foil is then calendered. Theseparator was microporous polypropylene (Celgard 2400) of 1 mil (0.025mm) thickness. The anode was a sheet of lithium metal.

TABLE I Cathode Composition Wet Cathode Slurry Dry Cathode (wt. %) (wt.%) Binder (Kraton G1651) 2.0 3.01 Hydrocarbon Solvent 13.4 0.0 (ShellSolA100) (ShellSol OMS) 20.2 0.0 FeS₂ Powder (Pyrox Red 325) 58.9 88.71Graphite (Timrex KS6) 4.0 6.02 Acetylene Carbon Black (Super P) 1.5 2.26Total 100.0 100.00

The anode, cathode, separators, and an insulating polypropylene tapewere spirally wound to the shape of the casing body. The spirally woundelectrode assembly was inserted into the open end of the casing. Thecasing was placed under vacuum, then the electrolyte was added to thecell while the case is under vacuum. The electrolyte added to the cellincluded a mixture of Li(CF₃SO₂)₂N (LiTFSI) salt (0.8 mols/liter)dissolved in a solvent mixture of 1,3 dioxolane (80 vol %) and sulfolane(20 vol %). Also, 0.1 wt. % pyridine was added to form the finalelectrolyte solution. The casing was then capped with a cap.

A metal tab 44 (anode tab) was pressed into a portion of the lithiummetal anode. The anode tab was pressed into the lithium metal at anypoint within the spiral. The anode tab was embossed on one side forminga plurality of raised portions on the side of the tab to be pressed intothe lithium. The opposite side of tab was welded to the inside surfaceof the closed end of the casing. The primary lithium cell had a PTC(positive thermal coefficient) device located under the end cap andconnected in series between the cathode and end cap.

In the test cells, the cathode contained on average 4.97 g irondisulfide (FeS₂, Pyrox Red 325) as cathode active material. The cellshad an interfacial surface area between anode and cathode with separatortherebetween of about 300 cm². The cells were balanced so that thetheoretical capacity of the anode was lower than the theoreticalcapacity of the cathode.

Specifically, the test cells were balanced so that the ratio of thetheoretical capacity of the anode to the theoretical capacity of thecathode was about 0.9. (The theoretical capacity of the anode is thetheoretical specific capacity of lithium metal, 3861.4 mAmp-hr/gram,multiplied by the weight in grams of the lithium and the theoreticalcapacity of the cathode is the theoretical specific capacity of FeS₂,893.5 mAmp-hr/gram, multiplied by the weight in grams of the FeS₂.)

The volume of pores in both separators was 0.3242 ml, the volume ofpores in the cathode was 0.4107 ml. The theoretical minimum electrolytevolume was calculated to be 1.11 ml. The cell performance was measuredusing an ANSI digital picture test at 1.05V cutoff. The cell performancewas plotted against the electrolyte fill ratio (defined as volume ofelectrolyte (v)/mass of cathode active material (m)). Referring to FIG.2, a ratio of greater than 0.33 ml/g led to performance improvements,which increased as the electrolyte fill ratio was increased up to 0.43ml electrolyte/g FeS₂ (or 2.14 ml electrolyte total in theelectrochemical cell).

For the ANSI digital picture test, after the fresh cells werepredischarged (by subjecting the cells to a the predischarge protocolincluding a series of cycles, each cycle consisting of about 2 Amp pulse“on” for 7 seconds followed by 20 seconds “off” to remove about 3% ofcell capacity), and stored for 14 days at ambient room temperature(about 20° C.), the cells were subjected to the digital picture testdesigned to simulate use in digital cameras.

ANSI Digital Picture Test

The digital camera test consists of the following pulse test protocolwherein each test cell was drained by applying pulsed discharge cyclesto the cell: Each cycle consists of both a 1.5 Watt pulse for 2 secondsfollowed immediately by a 0.65 Watt pulse for 28 seconds. This isrepeated 10 times followed by 55 minutes rest. Then the cycling isrepeated until the cutoff voltage is reached. The cycles are continueduntil a cutoff voltage of 1.05V is reached. The number of cyclesrequired to reach these cutoff voltages was recorded. (The number ofpulses reported consists of the high 1.5 Watt pulses, which correspondsto the number of pulsed cycles.)

OTHER EMBODIMENTS

While certain embodiments have been described, other embodiments arepossible. For example, electrochemical cells such as AAA, AAAA, C, D,and/or other sizes of batteries can be made where the volume of theelectrolyte is increased to compensate for the increase in void volumeduring battery discharge.

All references, such as patent applications, publications, and patents,referred to herein are incorporated by reference in their entirety.

Other embodiments are in the claims.

What is claimed is:
 1. A battery, comprising a housing, and within thehousing: (a) an anode comprising an alkali metal; (b) a cathodecomprising a mass (m) of a cathode active material selected from thegroup consisting of transition metal polysulfides having the formulaM1_(a)M2_(b)S_(n), wherein M1 and M2 are transition metals, a+b is atleast 1, and n is at least 2(a+b); and (c) a volume (v) of anelectrolyte, wherein the ratio v/m is at least 0.33 to at most 0.55ml/g.
 2. The battery of claim 1, wherein the mass (m) is at least 4.5 g.3. The battery of claim 1, wherein the cathode has a porosity of at most35%.
 4. The battery of claim 1, wherein the volume (v) of electrolyte isat least 1.4 ml and at most 2.2 ml.
 5. The battery of claim 1, whereinthe alkali metal is lithium.
 6. The battery of claim 5, wherein thelithium is alloyed with aluminum.
 7. The battery of claim 5, wherein thelithium metal is not alloyed with another metal.
 8. The battery of claim1, wherein the cathode further comprises a material selected from CuS,Cu₂S, FeS, CuO, Bi₂O₃ and combinations thereof.
 9. The battery of claim1, wherein the cathode active material comprises one or more materialsselected from FeS₂, CoS₂, NiS₂, MoS₂, Co₂S₉, Co₂S₇, Ni₂S₇, Fe₂S₇, Mo₂S₃,NiCoS₇, and combinations thereof.
 10. The battery of claim 1, whereinthe cathode active material is FeS₂.
 11. The battery of claim 1, whereinthe alkali metal is lithium, the cathode active material is irondisulfide.
 12. The battery of claim 1, wherein the electrolyte furthercomprises a lithium salt.
 13. The battery of claim 1, wherein thebattery is a primary battery.
 14. A method of using a battery,comprising: discharging but not recharging a battery comprising ahousing, and within the housing: (a) an anode comprising an alkalimetal; (b) a cathode comprising a mass (m) of a cathode active materialselected from the group consisting of transition metal polysulfideshaving the formula M1_(a)M2_(b)S_(n), wherein M1 and M2 are transitionmetals, a+b is at least 1, and n is at least 2(a+b); and (c) a volume(v) of an electrolyte; wherein the ratio v/m is at least 0.33 to at most0.55 ml/g.